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ON THE SEXUAL ORGANS OF THE CYCADACE.T;. 75
which therefore performs the function of a stigma, is entirely naked,
and secretes a viscous fluid. After a short period, the internal capacity
of the cone is entirely filled with cellular tissue, which afterwards
softens, and is partially reabsorbed. Mucilaginous channels (the paths
taken by the pollen-tubes) are formed in it, which terminate below the
wall of the embryo sac, in what have been called the areohe, beneath
which are situated the opercular rosettes of the corpuscles. (Plate XCI.
fi"-. 1-3, lU and 11, a section of the free summit in the direction of its
length.) The upper wall of the embryo-sac being situated at the level
where the nucleus becomes free, and where the base of the cone is
solidly united to the coat, the cone is anatomically separate from the
adherent portion of the nucleus, and as that becouies forced outwards
and compressed by the dilatation of the endospermic cavity, this trans-
verse separation becomes more and more distinct. Finally it witliers,
and it is afterwards found, particularly in fertilized fruits, applied as a
cap on the top of the endosperm. In this condition it formerly re-
ceived from some authors the very inexact names of vitellus or scittel-
lum. (Plate XCI. fig. 13 a, Plate XCII. fig. 11.)
The history of the embryo-sac or amnios is very complicated, and it
was not till after Hofmeister, Pineau (Annales des Sciences Nat.,
3me serie, ii. p. 83), and others had unravelled it in the Goniferce, that
I found it intelligible amongst the Cycadace/s. The exact time of the
first appearance of the embryo-sac I do not know, but it is quite certain
that it takes place at a very early period in the existence of the ovule,
and in the upper half of the adherent portion of the nucleus, termed
by Hooker the corpus nuclei. From its first appearance, the cavity of
the embryo-sac is filled with cells. At this period it is small and
spherical, antl its wall may be seen to consist of simple cellular mem-
brane. I have only twice had the opportunity of examining it in this
state, once in a Cycas, and once in a Zamia, The interior cellular
tissue next disappears, and the cavity enlarges, and becomes filled with
a mucilaginous fluid; from analogy with what takes place among
Conifei-cB, one would be led to believe that the period of fecundation
approaches at this point. The second stage now commences, and
as it is also completed in unfertilized ovules (fertilized ones have
not yet been observed in botanic gardens), there is no reason for
doubting that it is independent of fertilization. The free and rapid
development of cells produces a highly developed albumino-plastic